The present invention relates to dry shaving apparatus comprising: a drive source provided in a housing; a first shaving unit having a first outer cutter and a first undercutter mounted for relative movement therebetween; and a second shaving unit having a second outer cutter and a second undercutter mounted for movement beneath said second outer cutter.
Although this specification is primarily concerned with shavers having shaving units extending in a longitudinal direction provided with linearly oscillating inner cutters as described in U.S. Pat. No. 5,185,926 or German Patent DE 43 38 789 C2, it will be understood that the principles described may also readily be applied in dry shavers provided with rotating inner cutters as known by Japanese patent publication JP-A-5 317 535 or WO 96/02368.
In addition this application is also concerned with dry shaving apparatus provided with at least two shaving units being fixedly mounted on a shaving housingxe2x80x94U.S. Pat. No. 5,185,926xe2x80x94or mounted floatably in a shear head framexe2x80x94DE 43 13 371 C2xe2x80x94or mounted in a shear head being pivotably mounted on a shaver housingxe2x80x94WO/93/12916.
One example of linear dry shaving apparatus is known from WO 93/12916. This known apparatus includes in one embodiment three individual floating shaving units mounted in a pivotable head. The units are arranged in parallel with one unit constructed as a long hair cutter positioned centrally between two units constructed as short hair cutters. The spring biasing in the individual units is such that during use the cutter units can move up and down to follow the contours of the face and thus to improve contact with the skin during use.
It is also known from DE-B-1 003 629 to provide beneath a single perforate foil an array of four separate undercutters. The two outboard undercutters are driven together and separately from the two inboard undercutters. This allows the inboard undercutters to be driven in anti-phase with respect to the outboard undercutters to produce a degree of dynamic balancing and reduce vibration of the housing.
Japanese Application JP-B2-8-17859 discloses a reciprocatory electric shaver comprising a central main shaving unit, having an outer foil cutter and an inner cutter, and two trimmers on respective sides of the main cutter. According to this proposal, the undercutter of the main shaving unit is caused to reciprocate in anti-phase with the undercutters of the trimmers to improve dynamic balancing.
Moreover, it is also known from German patent No. 1 004 518 and from DE-A-23 09 342 to provide a shaver with a single foil-type cutter assembly and two comb-like trimmer assemblies on respective sides of the foil-type cutter assembly, where each trimmer assembly has a movable blade in contact with the skin, which blade is directly connected to the undercutter of the foil-type cutter assembly. This allows limited catching by the trimmers of long hairs missed by the foil-type cutter.
Although foil type dry shaving apparatus operates very effectively to remove stubble, problems sometime arise with hairs of a length representing two or three days beard growth. Such hairs no longer readily penetrate through the apertures of the foil and therefore are not cut by the interaction between the undercutter and the foil. Various attempts have been made over the years to combat this problem. For example, U.S. Pat. No. 2,309,431 discloses a dry shaver having a pair of shaving units in which not only the undercutters but also the outer skin-engaging cutters are caused to oscillate in anti-phase. By thus moving the cutting heads on the skin, the hair receiving openings were intended to move over the skin surface with a xe2x80x9cscanningxe2x80x9d action, so that all parts of the skin beneath the cutting head would be successively brought into register with the hair receiving openings. However, to avoid excessive discomfort it was considered inadvisable to reciprocate the outer cutting heads at more than 3,000 revolutions per minute although the undercutters were caused to reciprocate at from 3 to 5 times that frequency. Moreover, making use of a somewhat complex cam operated drive assembly, the outer cutters were reciprocated in opposite directions which produces a stationary skin zone mid-way between the cutters.
U.S. Pat. No. 4,174,569 discloses another proposal in which an outer cutter shearing cutter is caused to oscillate in contact with the skin, whilst a further cutter oscillates beneath the outer cutter. As in U.S. Pat. No. 2,309,431, the frequency of oscillation of the inner cutter was considerably higher than that of the outer cutter.
These attempts to improve the penetration of long beard hairs through a perforated outer cutter have not been particularly successful. Moreover, the prior art seems to contain no appreciation of any possible interaction between adjacent shaving units.
An object of the invention is to provide a dry shaving apparatus in which the penetration of hairs through a perforate outer cutter is improved.
Another object of the invention is to provide dry shaving apparatus in which the hairs are positioned optimally for cutting following penetration of the outer cutter.
Another object of the invention is to provide dry shaving apparatus in which individual cutters may be driven with a desired stroke and phasing in a simple manner.
According to one aspect of the invention the dry shaver initially defined is characterised in that the first outer cutter is mounted for oscillatory movement to serve as a skin agitation member; and the first outer cutter and the second undercutter are coupled to the drive source to be oscillated at the same frequency.
Preferably, the first outer cutter is displaced in phase from the second undercutter by an angle in the range xe2x88x92120xc2x0 to 120xc2x0.
In one embodiment, the first outer cutter is driven in phase with the second undercutter.
In another embodiment, the first outer cutter leads or lags the second undercutter in phase by substantially 90xc2x0.
Preferably, a third shaving unit for short hairs is provided and comprises a third perforate outer cutter and a third undercutter mounted for oscillatory movement beneath the third outer cutter, the first unit being provided between the second and third shaving units.
In one embodiment, the first outer cutter lags the third undercutter by substantially 90xc2x0.
According to a further aspect of the invention, there is provided a dry shaving apparatus comprising: a drive source provided in a housing; a first shaving unit coupled to the drive source and having a first outer cutter and a first undercutter mounted for relative movement therebetween; and at least one further shaving unit having a second outer cutter and a second undercutter coupled to the drive source and mounted for movement beneath said second outer cutter; characterised in that: at least the first outer cutter of the first shaving unit is coupled to the drive source and is mounted for oscillatory movement to agitate the skin under a further of the shaving units.
It will be understood that by activating the skin using the active unit, the skin surface is caused to move to and fro across the skin-engaging surface of the or each inactive unit. This aids penetration of hairs into the or each inactive unit and enhances the chance that the hairs will be cut with minimal discomfort. Further enhancement may be achieved by phase or frequency adjustment as will be described.
In one embodiment of the invention, two inactive shaving units are provided on respective sides of an active shaving unit. The outer cutter of the active unit may then be driven at the same frequency as the undercutters of the inactive units (synchronous operation) or at a different frequency (asynchronous operation). Where the frequency is the same, the phasing of the undercutters in the inactive units may be optimised with respect to the outer cutter of the active unit.
It is presently believed that the best arrangement is for the undercutter of one inactive unit to lag by a small angle close to zero (for short hairs) and the undercutter of the other inactive unit to lead by 90xc2x0 (for long hairs). However, the exact phasing may be set by experiment to optimise the shaving performance. It may be preferred to drive the undercutter of one inactive unit in phase with the outer cutter of the active unit and to adjust the phase of the undercutter of the other inactive unit to be optimum for long hairs (leading by about 90xc2x0) or, for practical reasons of construction, to drive the undercutters of both inactive units in phase with the outer cutter of the active unit.
Where the outer cutter of the active unit is driven at a different frequency (higher or lower) than the undercutters of the inactive units, no phase adjustment is of course either necessary or possible, since a cyclically varying phase condition will be present.
In a simplified embodiment, only two shaving units are provided, one active and the other inactive. Here again two possibilities exist: either the outer cutter of the active unit is driven at the same frequency as the undercutter of the inactive unit, or at a different higher or lower frequency. Where the frequencies are the same, phase adjustment is possible. For reasons of simplicity, one construction provides for the outer cutter of the active unit to be driven in phase with the undercutter of the inactive unit. In such a construction, the undercutter of the active unit may be static or may be driven in anti-phase with the outer cutter.
In any of the embodiments, it may be advantageous to adapt the skin-engaging surface of the outer cutter in the active unit for enhanced grip on the skin, e.g. by roughening or by applying a high-friction coating. Moreover, to maximise the amount of skin movement over the inactive units, it may be advantageous to provide the skin-engaging surface of the (or each) inactive unit with a low-friction coating. In some circumstances, it may prove advantageous to provide the skin-engaging surface of the active unit with a low-friction coating.